1. Field of the Invention
The present invention relates to a method for manufacturing a thermoplastic resin film, and an optical compensation film and a polarization plate for liquid crystal display panels, and particularly to a technology to manufacture by a melt-film forming method an unstretched thermoplastic resin film for a stretched thermoplastic resin film having a suitable quality for liquid crystal display panels.
2. Description of the Related Art
Thermoplastic resin films such as cellulose acylate films are formed by melting a thermoplastic resin and extruding the thermoplastic resin to a die by an extruder, and cooling and solidifying the melted resin as a sheet-like melted resin from the die. Then, the thermoplastic film formed as a film is stretched in the longitudinal (length) direction and in the transverse (width) direction to develop the in-plane retardation (Re) and the thickness-direction retardation (Rth), and is used as a retardation film for liquid crystal display elements, and is put into practice for enlarged viewing angle (for example, see National Publication of International Patent Application No. 6-501040).
Here is proposed a film forming apparatus of touch roll type in which thermoplastic resin films unstretched (prior to stretching) are manufactured by nipping a sheet-like melted resin discharged from a die between an elastic roller and a cooling roller. According to the film forming apparatus, a sheet-like melted resin can be planarly pressed by nipping the sheet-like melted resin between an elastic roller and a cooling roller, improving the precision in thickness of thermoplastic resin films.